Misfire/backfire

Hey guys, I have the vehicle listed above it has a big block in it. Had a backfire, changed out the plugs and fuel filter. Sprayed a couple squirts of carburetor cleaner in the throttle body. Now she idles something awful! And still backfires. I cleaned the K&N air filter and I did not check with a gauge but I did push down on the Schrader valve and heard the push of air and plenty of fuel came out. Fuel filter had quite a bit of pressure as well. Thoughts?